WILLIAM & DEBORAH HILLYARD

Solar System -

The Asteroid Belt

The Largest Asteroids

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1 Ceres
Giuseppe Piazzi discovered 1 Ceres in 1801, and at first it was considered to be the eighth planet; Neptune and Pluto had not been discovered.  It was the first asteroid to be discovered, and is the largest found to date.  It is near spherical, 975 km (606 miles) across at the equator, with a polar diameter of 909 km (565 miles).  It is the only asteroid considered a dwarf planet, although it is the smallest dwarf planet.  Its shape suggests that it has a differentiated interior, similar to the Earth and other rocky planets, with a rocky inner core and a thin, outer crust.  Ceres may have large deposits of water ice under its crust because as its density is rather low.  There is also evidence that the surface contains water-bearing minerals. It is possible that Ceres could have more water than all the fresh water on Earth, but as a layer of water ice in the mantle wrapped around the core.  Ceres contains almost a third of the mass of the entire asteroid belt.  Planetary astronomers generally believe Ceres formed as a protoplanet in the early days of the solar system, but did not merge with other protoplanets in the same way that, for example, the Earth did.  Its orbit takes it from 2.5468 AU to 2.9858 AU from the Sun.  It takes 4.6 years to go once around the sun. 

4 Vesta

Discovered not long after Ceres, in 1807, 4 Vesta was the fourth found, and is the second largest asteroid, by weight.  It is elongated, about 580 km by 460 km (360 by 285 miles).  It represents about 9% of the total mass of the asteroid belt objects.  Within the last billion years, Vesta suffered a catastrophic collision that left a crater at its south pole that is about 460 km across, and blew about 1% of its entire mass into space.  The remaining fragments, at least 235 found to date, together with Vesta, comprise the Vesta group of asteroids.  Some fragments are believed to be the source of the HED meteorites, many of which found their way to the Earth and have been recovered.  Its slightly eccentric orbit takes it from 2.151 AU to 2.572 AU from the Sun.  It takes 3.63 years to go once around the sun. 

2 Pallas

2 Pallas was discovered in 1802, and is about 580 km by 500 km (average 544 km), making it comparable in size to Vesta, but it is substantially lighter being about 7% of the mass of the asteroids.  It has an eccentric orbit around the sun, varying from 2.132 AU to 3.412 AU, which is substantially inclined to the plane of the main asteroid belt by nearly 35°. 

10 Hygiea

10 Hygiea, discovered in 1849, is the fourth largest of the asteroids, and is also elongated, about 530 x 407 x 370 km (average 431 km).  Its orbit is somewhat eccentric, taking it from 2.77 AU to 3.507 AU, and it goes around the Sun every 5.56 years.  It is the largest asteroid in the Hygiea family representing more than 90% of the mass of the family.

704 Interamnia

704 Interamnia is about 350.3 x 303.6 km, with an average diameter of 326 km.  It represents about 1.2% of the total mass of the asteroid belt.  Its orbit is moderately eccentric varying between 2.601 AU and 3.522 AU, and takes about 5.36 years to go around the Sun. 

52 Europa

52 Europa is an elongated asteroid some 360 x 315 x 240 km.  It has a low density, and is porous.  Its slightly eccentric orbit takes it from 2.785 AU out to 3.417 AU, and it goes once around the Sun every 5.46 years. 

511 Davida

511 Davida is an elongated asteroid some 357 x 294 x 231 km.  Its slightly eccentric orbit takes it from 2.58 AU out to 3.754 AU, and it goes once around the Sun every 5.64 years.  It is believed to have a massive impact crater on its surface about 150 km in diameter. 

87 Sylvia

87 Sylvia is a low density, elongated asteroid some 384 x 262 x 232 km.  Its slightly eccentric orbit takes it from 3.213  AU out to 3.768 AU, and it goes once around the Sun every 6.52 years.  Sylvia has two small moons called Romulus and Remus.  Romulus is about 18 km in diameter and orbits at a distance of 1356 km every 87.59 hours.  Remus, the second moon is 7 km in diameter and orbits at a distance of 706 5 km every 33.09 h.

65 Cybele

65 Cybele is about 302 x 290 x 232 km.  Its slightly eccentric orbit takes it from 3.073 AU out to 3.794 AU, and it goes once around the Sun every 6.36 years. 

15 Eunomia

15 Eunomia is an elongated asteroid some 357 by 255 by 212 km.  Its slightly eccentric orbit takes it from 2.149 AU out to 33.138 AU, and it goes once around the Sun every 4.3 years.